试图了解over()和分区 [英] Trying to understand over() and partition by

问题描述

我试图通过包裹在我头上的功能来解决问题.这是一个我不明白的例子.

I am trying to get the over and partition by functionality wrapped around my head. Here is an example that I just do not understand.

这是我的数据:

SALESORDERID       ORDERDATE 
43894              08/01/2001 
43664              07/01/2001 
43911              08/01/2001 
43867              08/01/2001 
43877              08/01/2001 
44285              10/01/2001 
44501              11/01/2001 
43866              08/01/2001 
43895              08/01/2001 
43860              08/01/2001

当我运行此查询时:

select Row_Number() over(partition by orderdate order by orderdate asc) 
    as Rownumber, salesorderid, orderdate
from test2
order by rownumber

这是我得到的结果:

ROWNUMBER     SALESORDERID       ORDERDATE 
1             43664              07/01/2001 
1             43911              08/01/2001 
1             44109              09/01/2001 
1             44483              11/01/2001 
1             44285              10/01/2001 
2             43867              08/01/2001 
2             44501              11/01/2001 
3             43895              08/01/2001 
4             43894              08/01/2001 
5             43877              08/01/2001 

有人可以向我解释此查询.我对SQL并不陌生，但是我一直在苦苦挣扎的窗口工作，无法解决这个问题.

Can someone explain this query to me. I am not new to SQL but windowing I have been struggling with and can't get my head wrapped around this.

推荐答案

尝试按订购日期订购，您会更轻松地看到结果

Try ordering by order date, you'll see the results more easily

select Row_Number() over(partition by orderdate order by orderdate asc) 
    as Rownumber, salesorderid, orderdate
from test2
order by orderdate;

应该给出(为了清楚起见，我添加了空白行)

should give (i've added blank lines for clarity)

ROWNUMBER     SALESORDERID       ORDERDATE
1             43664              07/01/2001

1             43911              08/01/2001
2             43867              08/01/2001
3             43895              08/01/2001
4             43894              08/01/2001
5             43877              08/01/2001

1             44109              09/01/2001

1             44285              10/01/2001

1             44483              11/01/2001
2             44501              11/01/2001

您会注意到结果被划分为分区"，每个分区都是具有相同订购日期的行的集合.这就是按订单日期划分"的意思.

You'll notice that the result is divided into 'partitions', each partition being the set of rows with identical orderdates. That is what 'partition by orderdate' means.

在分区中，行按照orderdate排序，如'((按orderdate排序，按orderdate asc)排序.这不是很有用，因为分区中的所有行都将具有相同的orderdate.因此，分区中行的顺序是随机的.尝试在partition by子句中按salesorderid进行排序，以获得更可重复的结果.

Within a partition, the rows are ordered by orderdate, as per the second clause of '(partition by orderdate order by orderdate asc)'. That isn't very useful, as all rows within a partition are going to have the same orderdate. Because of that, the ordering of the rows within a partition is random. Try ordering by salesorderid within the partition by clause to have a more reproducable result.

row_number()仅返回行在每个分区内的顺序

row_number() just returns the row's ordering within each partition

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